6.1.1 Cellular Control

Question 1

Defintion of gene mutation and the 3 types

Answer 1

A change in the sequnce of base pairs that may result in an altered polypeptide
Insertion, subsitition, deletion

Question 2

Why may a mutation result in no change to the polypeptide

Answer 2

Genetic code is degenerate so serval different triplets code for the same amino acid
Lots of the interaction in polypeptides depend on wether the amino acid is hydrophobic or hydrophilic, a wrong amino acid can still have the correct effect

Question 3

Insertion

Answer 3

A nucleotide is randomly inserted into the DNA sequence
This change has a knock on effect as every bass after the insetion is wrong (known as frameshift mutation)
This may dramatically change the amino acid sequence produces from this gene and therefore the abilty of the polypeptide to perform its function.

Question 4

Deletion of nucletoides

Answer 4

A nucleotide is randomly deleted from the DNA sequence
Changes the amino acid that would have been coded for, also has a knock on effect as every base is 1 position forward
Frameshift mutation
Dramatically changes polypeitde

Question 5

Substitution

Answer 5

A base in the DNA sequence is swapped for a different base, only changes 1 amino acid, no knock on effect
Silent mutation - does not change amino acid
Missense mutation - alters a single amino acid in the polypeptide chain
Nonsense mutation- creates a premature stop codon

Question 6

Effects of mutation can be

Answer 6

Harmful
Neutral
Beneficial

Question 7

Controls of gene expression ( 4 stages)

Answer 7

Transcriptional control
Post transcriptonal control
Translational control
Post translational control

Question 8

Structure of the lac operon

Answer 8

Regulatory gene -promoter-operator-structrual genes ( z and y)
Repressor protein is bound to promoter and operator
When lactose is pressent it enters the ecoli and binds to the repressor causing it to release, RNA polymerase binds to operator and begins transcription
The structural genes are transcribed and the enzymes are synthesised

Question 9

Enzymes transcribed by the lac operon

Answer 9

Lactose permease - moves into the membrane of the ecoil making it easier for lactose to enter the cell
Lactase - breaks down lactose - glucose and galactose , glucose is used by the cell

Question 10

Types of gene and what they code for

Answer 10

Structural gene - codes for protein that has a function within a cell e.g enzymes, hormones
Regulatory genes - codes for a protein that control the expression of structural genes

Question 11

Transcription factors and how they work

Answer 11

Protiens that bind to spefic reigons of DNA ( promoter reigons) to control the transcription of DNA
Binding can either allow or prevent transcription from taking place
Binding of transcription factors will either increase or decrease the rate of transcription of a gene

Question 12

Difference between exons and introns

Answer 12

Exon - expressed region of DNA, codes for amino acids

Intron - intragenic reigon ( non coding sequences)

Question 13

Why post transcriptional control is needed

Answer 13

When DNA is transcribed both exons and introns aretranscribed
The intron sections need to be removed from the pre-mRNA molecule
Exons fuse together to form mature mRNA that is ready for translation
This process is called splicing
Primary MRNA is also edited

Question 14

Control at the post translational level

Answer 14

Involves modfiication to the protiens that have been synthesised e.g.
Addition of non protien groups such as carbohydrate chains , lipids, phosphates
Modifying amino acids and the formations of bonds such as dislufide bridges
Some polypeptides require activation by cyclic AMP
Cyclic AMP acitvates protein kinases which itself is a precursor enzyme which acitvates other proteins

Question 15

What are Homeobox genes

Answer 15

Group of genes that all contain a homeobox, a homeobox is a section of DNA 180 base pairs long codes for a protein transcription factor that is exactly 60 amino acids long.
They attach to DNA at specific reigons and regulate the transcription of genes by turning various genes on and off
These reigons are highly conserved becuase any mutation would lead to the organism not surviving
Homeobox genes are responsible for the genetic control of the development of body plans

Question 16

Hox genes

Answer 16

Are one group of homeobox genes only present in animals
Are a set of transcription factors that are only present in animals and are responsible for the correct positioning of body parts
Hox genes are found in gene clusters, mammals have four clusters
The order in which they appear along the chromosome is the order in which their effects are expressed on the organisms

Question 17

Protein kinases

Answer 17

Enzymes that catalyse the additon of phosphate groups to proteins
The additon of a phosphate group changes the tertiary structure and therefore the function of the protein
Protein kinases are activated by cyclic AMP

Question 18

What is apoptosis

Answer 18

Programmed cell death

Question 19

Importance of mitosis and apoptosis

Answer 19

Constant replacing and destruciton of cells in early development
Some cells produced by mitosis are no longer needed therefore they are destroyed
E,g fingers and toss are developed as single combined units then are seperated later by programmed cell death

Question 20

How can genes which regulate the cell cycle and apoptosis be effected

Answer 20

Internal cell stimuli - internal factors that affect apoptosis and cell cycle
irrepareable genetic damage, RNA decay : these factors can initiate apoptosis in cells that are undergoing cell stress
External cell stimuli - external factors that affect apoptosis and cell cycle
Presence of signaliing molecules: cytokines, hormones
Virsus and bacteria, damaging cells faster than they can be replaced
Cells often respond to such stressful stimuli by activating pathways to increase their chance of survival or initiating apoptosis

Question 21

Relationship between regulatory and structural genes

Answer 21

Regulatory genes control the expression of structural genes

Question 22

Function of DNA and RNA polymerase

Answer 22

DNA polymerase - involved in semi conservative DNA replication, works on 2 strands
RNA polymerase - make m/t/r RNA and involved in transcription, works on 1 strand

Question 23

Why meiosis needs 2 divisions

Answer 23

Diploid to haploid 46 chromosomes to 23

Separate homologous pairs and then sister chromatids

Question 24

Role of PCR

Answer 24

amplify the volume of DNA trying to be sequenced

Giving DNA sections with a range of different lengths

Question 25

Role of electrophoresis

Answer 25

• Allows DNA sample to be spread out based on length / size

- order of bases can be read

Question 26

Role of restriction enzymes

Answer 26

Cut DNA into fragments so it can be read

Question 27

Why genome has to be fragmented before sequencing

Answer 27

Genome is too large to sequence as a whole

Sequencing is more accurate when cut

Question 28

How has the knowledge of apoptosis helped science

Answer 28

Allows us to understand and treat tumours and autoimmune disease

Question 29

Where does RNA polymerase bind on the lac operon

Answer 29

Promoter region